More from WebMD

Discovering that you are expecting is emotional and exciting, but it can also be worrisome. You may be anxious about many things -- from what type of mother you will be to the economics of raising a family -- in addition to all the changes going on in your body.

What’s normal? What's not? When should you call the doctor and when should you take a deep breath?

To help put your mind at ease, WebMD talked with experts about serious symptoms that may occur during the first trimester, what they may mean, and what you should do about them. Of course, if you're concerned about anything during your pregnancy -- even if it's not one of these symptoms -- contact your doctor.

What it may mean: “Some spotting is normal, but heavy bleeding could be a sign of miscarriage or ectopic pregnancy,” says Natali Aziz, MD, a maternal-fetal medicine specialist at Lucile Packard Children's Hospital in Palo Alto, Calif. “The brighter red the bleeding, the more significant it is,” she says. “The darker the blood color, the more likely it is blood from an older bleed leaving the body,” she says.

“If you have bleeding and bad cramping similar to period cramps, this can be a sign of threatened miscarriage,” says Manju Monga, MD, the Berel Held Professor and the division director of maternal-fetal medicine at the University of Texas Health Sciences Center in Houston. “If this is coupled with sharp lower abdominal pain, it may be a sign of ectopic pregnancy,” a serious complication that occurs when the fertilized egg implants outside the uterus, usually in the fallopian tubes.

What to do: “Call your doctor,” Monga says. “Your doctor will likely do an ultrasound, an exam, and some blood work based on your symptoms,” she says.

Bottom line: “Most spotting or light bleeding is not a serious problem or condition, but you don’t want to ignore it if it is associated with cramping, heavy bleeding, or abdominal pain,” she says. “You are always better safe than sorry.”

Serious symptom No. 2: Excessive nausea and vomiting

Some nausea and vomiting during your first trimester is normal, but if it crosses the line and becomes excessive, it can have serious consequences.

What it may mean: “Vomiting that interferes with your day-to-day activities can lead to weight loss, dizziness, dehydration, and an imbalance of electrolytes,” Aziz says.

What to do: “Tell your doctor,” she says. “You may need hospitalization to treat the dehydration, and many medications are available to control nausea."

Bottom line: “Nausea and vomiting are normal occurrences during pregnancy, but the extremes can cause problems,“ says Stanley M. Berry, MD, corporate chairman of obstetrics and gynecology at William Beaumont Hospital in Royal Oak, Mich. “The majority of women who have nausea and vomiting in their first trimester will go on to have normal, healthy pregnancies.”

Serious symptom No. 3: High fever

A fever greater than 101 degrees Fahrenheit or 38 Celsius during pregnancy may be serious.

What it may mean: “We know that pregnant women are at higher risk for more severe flus, including swine flu,” Azis says. High fever during the first trimester can also be associated with certain birth defects. One is neural tube defects because the neural tube is forming during the first trimester.

Fevers during pregnancy that are accompanied with rash and joint pain may be a sign of infection such as cytomegalovirus (CMV), toxoplasma, and parvovirus, she says. “CMV is the most common cause of congenital deafness, and it is not as uncommon as we think,” she says.

What to do: “Report any fever plus upper respiratory symptoms, body ache, and flu-like symptoms or rashes and joint pain to your doctor,” Aziz says. “It is extremely important to be evaluated and to bring down your fever with Tylenol (acetaminophen).”

Bottom line: “Pregnant women are at greater risk of severe illness including hospitalization, intensive care unit admissions, and death from influenza, especially the H1N1 flu, because our bodies hadn’t seen it before,” she says. Prevent this by getting vaccinated.

Serious symptom No.4: Vaginal discharge and itching

“These may be signs of treatable infections or sexually transmitted diseases that can have important consequences in pregnancy,” Aziz says.

What this may mean: “These can cause pre-term delivery or infection to the fetus,” she says

What to do: Report it to your obstetrician ASAP, Aziz says.

Bottom line: Don’t be shy. Let your ob-gyn know what is going on down there because treating the underlying problem can be a lifesaver.

Serious symptom No. 5: Pain or burning during urination

What this may mean: “These can be signs of bladder or urinary tract infections and if left untreated, they can lead to more serious illness, infection, pre-term labor, and pre-term birth,” Aziz says.

What to do: Tell your doctor ASAP, she says.

Bottom line: Treating the infection can relieve your pain, and help assure a healthy pregnancy.

What it could mean: “This could mean a blood clot,” Aziz says. “Pregnancy is a state of hypercoagulation, which means that pregnant women are at higher risk for blood clots in the lower extremity or brain,” she says. A blood clot in the calf may result in pain or swelling and can result in a blood clot that travels to the lung which could be fatal. A blood clot in the brain may be heralded by a severe headache, while a blood clot in the lower extremity is often marked by sharp pain, redness, and swelling. A blinding headache can also be caused by high blood pressure or a sign of a malformation in the brain.

What to do: Call your obstetrician ASAP.

Bottom line: Women who have a history of blood clots should discuss preventive treatment with their doctor before pregnancy or immediately after they find out they are expecting, she says.

Serious symptom No. 7: Exacerbations of underlying diseases

Women who have certain pre-existing medical conditions, such as thyroid disease, diabetes, high blood pressure, asthma, and/or lupus, need to be alert and aware of any changes in their condition during pregnancy.

What it may mean: If your underlying disease is flaring or not well-controlled, it can have serious consequences for your health -- and your baby’s. For example, “if your thyroid hormone is too high or low, you can be at an increased risk of miscarriage,” says Gayle Olson, MD, a maternal fetal specialist at the University of Texas Medical Brach in Galveston. Or, “if your blood sugar levels are not tightly controlled, you may be at increased risk of miscarriage or fetal abnormalities,” she says.

The bottom line: “Any flare in an underlying condition is a red flag and should be followed up,” she tells WebMD.

Most women will have healthy pregnancies, Berry says, so try to enjoy your pregnancy. “Stress is no good and the more positive the attitude, the better things are for mom and baby,” he says. Good prenatal care, such as regular doctor’s visits, a healthy diet, proper rest, and taking your prenatal vitamins are also essential, he says.